1. Field of the Invention
The invention relates to the field of pulsed electron sources and devices that make use of such sources, notably gas lasers with electronic excitation or X-ray pulsed pre-ionisation. A pulsed electron source emits an electron beam under the effect of ion bombardment.
2. Description of the Related Art
Reference may be made to the publications FR 2 204 882 or FR 2 591 035. The device comprises an ionisation chamber and an acceleration chamber communicating with the ionisation chamber through a grid. A preliminary discharge takes place in the ionisation chamber. Some of the positive ions thus created are accelerated towards a cathode located in the acceleration chamber. The accelerated ions bombard the cathode and cause the secondary emission of electrons. The accelerated secondary electrons, being repelled by the negative voltage applied to the cathode, then form an electron beam extracted through the grid between the two chambers.
In fact, it tends to become more and more difficult to trigger the discharge in the ionisation chamber as the use of the device continues. The discharge is thus initiated progressively later and there is a danger that it will occur at the same time as the negative voltage impulse applied to the cathode. The simultaneous application of the positive voltage in the ionisation chamber and of the negative voltage in the acceleration chamber risks causing a breakdown or even destruction of the device and the systems for which the device is used. The delayed triggering of the discharge will in any case cause a deterioration in the characteristics of the electron beam obtained as it leaves the source. Natural and hence uncontrolled delaying of the triggering of the discharge in the ionisation chamber is unsatisfactory.